soil biodiversity: why we need to think big to care for a ... · soil biodiversity: why we need to...
TRANSCRIPT
• Gerard Govers, Dept. Earth and Environmental Sciences, KU Leuven
Soil biodiversity: why we need to think big to care for a
small world
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Biodiversity is a hot topic
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There is a biodiversity crisis
• Extinction rates of species 10-100
times higher than background
• Extinction rates accelerating
• 1 million species threatened (to
varying degrees)
• Also non-threatened species suffer
decline in numbers and range and
local populations go extinct.
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Attention for biodiversity is growing
Google ngram
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As well as for soil biodiversity
Google ngram
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But, comparatively, soil biodiversity gets far less
attention
Google ngram
• 1 m² of surface area harbors, in
general, > 10000 below-ground
species (De Deyn and Van der
Putten, 2005)
• Below ground biodiversity is of the
same order of magnitude than above
ground biodiversity.
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Nevertheless, soil biodiversity is quantitatively
important
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Number of aboveground and belowground species
(De Deyn and Van der Putten, 2005)
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Human activity does not only reduce aboveground
biodiversity
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Soil biodiversity also suffers from (intensive)
agriculture
Tsiafouli et al., 2014
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And this has effect on soil ecosystem functioning
Bender et al., TREE
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This is not surprising: below ground processes mimic,
to some extent, above ground processes
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If biodiverse forest is converted to grazing land, you
do not only lose aboveground biodiversity but also
belowground biodiversity
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The ‘biological machine’ in the soil becomes simpler
Wall et al., 2015
• Decreased resilience to shocks (droughts, heat waves)
• Increase of negative environmental effects, e.g. due to less effective
denitrification (loss of nitrates and N2O)
• Human health
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Losing soil biodiversity may have important
implications
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Nitrogen use efficiency: interaction between
biodiversity and treatment (Ouedraogo et al., 2006)
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Human health
• Contacts with soil micro-organisms lessens allergic reactions
• But may also provide opportunities for soil-based pathogens
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Possible effects of a low of soil biodiveristy
• There is, to the best of my knowledge, *no* information whatsoever on the
relationship between soil biodiversity and agricultural yields
• Thus, the statement ‘we need a high soil biodiversity for food production’ does
not seem to hold.
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Important
• Rule 1: reduce physical disturbance
• Rule 2: reduce agricultural intensity
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We know that we can lessen negative effects of
agriculture on soil biodiversity
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Soil biodiversity fares better under low-intensity
systems
Tsiafouli et al., 2016
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(Soil) biodiversity fares better under organic
agriculture
Hole et al., 2015
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A keystone publication:
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Maeder et al., 2002
Red=conventional
Green= ‘biodynamic’
• Yes, at the field scale
• But is that enough ?
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Will low-intensity/organic agriculture increase soil
biodiversity ?
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The elephant in the soil biodiversity room: low
intensity agriculture will result in lower yields. Effects
of agriculture on aboveground biodiversity are related
to yield, not to the management system.
Gabriel et al., 2013
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The elephant in the soil biodiversity room: low
intensity agriculture will result in lower yields
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Intensive systems see (understandably) a larger yield
reduction
De Ponti et al., 2012
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Current analysis of soil biodiversity focuses on
agricultural land
• But wait….what will happen at the landscape scale ?
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No doubt that a reduced intensification will locally
enhance soil biodiversity
• reduce the yields per surface area
• Therefore increase the need for agricultural land
• Thus, we will have to use additional natural land as agricultural land to meet
our needs for food, fiber (and fuel)
• This means that we will have more land with reduced soil biodiversity
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Reduced agricultural intensity will…
• Sharing (reduced intensity agriculture in combination with biodiversity
preservation) is better
• Sparing (intensive agriculture with high yields and low biodiversity in
combination with larger areas not affected by agriculture) is better
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Two possibilities: sparing vs. sharing
Forest
Low Int Ag
High Int Ag
Forest
Low Int Ag
High Int Ag
Forest
Low Int Ag
High Int Ag
Land use distribution Soil biodiversity
a. Initial land use
b. Deforestation (sharing)
c. Intensification (sparing)
Sparing is better
Forest
Low Int Ag
High Int Ag
Forest
Low Int Ag
High Int Ag
Forest
Low Int Ag
High Int Ag
Land use distribution Soil biodiversity
a. Initial land use
b. Deforestation (sharing)
c. Intensification (sparing)
Sharing is better
For aboveground biodiversity the jury has decided
Phalan et al., 2011
Far more species benefit
from sparing than from
sharing
Sparing is the better solution to an impossibledilemma: we cannot provide food and preserve all
biodiversity
• We do not know !
• But it is, in my view, highly likely….
• Hypothesis: soil biodiversity is, in natural conditions, far larger than soil
biodiversity on agricultural land
Is this also true for soil biodiversity ?
• Preservation of soil biodiversity needs a perspective that is broader than the
agricultural field
• Landscape-scale preservation of soil biodiversity may not be optimally served
by optimising soil biodiversity on agricultural land
• It may be better to forsake some soil biodiversity on agricultural land to
preserve soil biodiversity elsewhere in the landscape
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Conclusions
• NO !
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Does this mean we should not worry/think about soil
biodiversity on agricultural land ?
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The dream of many soil scientists: ecological
engineering
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And it already works: rhizobium inoculation of soybean
• Assessing/evaluating the impact of agriculture on soil biodiversity requires a
landscape perspective. We may gain more by land sparing rather than land
sparing
• This does not mean that soil biodiversity on agricultural land should not be
considered. On the contrary we may realise important gains by manipulating it
to optimise the growing environment of agricultural plants
• However (tentative): the value of soil biodiversity per se on agricultural land
may not be our primary concern.
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Conclusions